The present invention generally relates to heat management systems for high power electronics equipment, and more particularly to a thermal bus system for a cabinet housing high power, high thermal profile electronic components and systems.
In many electronic systems, the efficient cooling of electronic components has become a significant problem. With the advent of large-scale integrated circuit (IC) modules containing many thousands of circuit elements, it has become possible to pack great numbers of electronic components together within a very small volume. As is well known, these integrated circuit modules generate significant amounts of heat during the course of their normal operation. Since most solid state devices are sensitive to excessive temperatures, a solution to the problem of the generation of heat by large scale IC""s in close proximity to one another has become of increasing concern to industry.
A typical prior art approach to cooling electronic components is to direct a stream of cooling air across the modules and/or cards carrying such devices. Several disadvantages to this approach have been identified, including: high pressure drop; uniformity of component form factors; placing the components containing the integrated circuits further apart on the circuit cards; increasing the distance between circuit cards; and increasing the volume and velocity of cooling air directed over the components. This required increase in volume and velocity of cooling air requires special considerations in the design of the housings containing the circuit cards and in the mechanical systems for delivering the cooling air. Also, the air quality(moisture content, contamination, etc.) must be tightly controlled to inhibit corrosion, loss of cooling effectiveness, etc. Thus, cooling of components by this means necessitates a number of compromises to the overall system that prevent its use in many systems.
Increases in the sophistication of electronic systems has brought about denser packaging of electronic components with attendant increases in power density and total card power. This has brought about the evolution of other techniques for cooling card-mounted electronic components. For example, one technique includes the use of solid metal thermal mounting cards or plates which conduct the heat dissipated by electronic components to a heat sink (cold plate) disposed at the edge of each card. Such an approach, however, results in a large thermal resistance from the component mounting surface to the heat sink, which causes high component temperatures.
In another known technique for cooling electronic systems, a two-phase loop thermosyphon is used to bus thermal energy away from the electronic components. More particularly, two-phase loop thermosyphons are devices that use gravity to maintain two-phase fluid circulation during operation. Each loop thermosyphon has an evaporator, where vaporization occurs when it is heated, a vapor tube (or line) where the vapor flows to a condenser, a cooled condenser, where condensation takes place, and a liquid return line (transport lines). Sometimes a capillary structure is used in the evaporator to reduce its thermal resistance. Significantly, prior art thermosyphon evaporators must have a vertical orientation so that the entire evaporator and capillary structure are flooded with liquid, which in turn boils when the evaporator is heated. This means that there is a liquid pool in the evaporator, and it is the boiling of that pool that is the main heat transfer mechanism in thermosyphon evaporators. Unfortunately, pool boiling heat transfer has been found to be less effective than vaporization from the surface of a porous structure, in terms of the thermal resistance.
Various other techniques for cooling electronics equipment in a cabinet are disclosed in the prior art, for example, U.S. Pat. No. 4,323,914, issued to Berndlmaier et al., discloses the removal of heat from a Large Scale Integrated Circuit semiconductor package via a thermal conductive path including a thermally conductive liquid. The integrated circuit chips are flip chips bonded to a substrate having a printed circuit and raised contact pads serving to interconnect contact areas on the chip. A metal or ceramic cover engages the perimeter of the substrate and encloses the chips (or chip). The thermal liquid is contained within the cavity defined by the cover and substrate. The chips (or chip) and the flip chip connections are protected from contamination and the deleterious effects of the thermally conductive liquid by a parylene film enveloping them.
U.S. Pat. No. 4,366,526, issued to Lijol et al., discloses a circuit card for high-density packaging of electronic components for use in high power-density card racks in computer and other electronic and avionic systems. The card has an all metal construction with an elongated planar body portion for the mounting of electronic components on opposite sides, and has a heat pipe located along the edges of one elongated side and two ends. A connector for making the required electrical connections to the electronic components is provided along the edge of elongated side. Edge tabs on the ends of the card permit the card to be installed into a card rack in electronic equipment. The elongated portion of the heat pipe serves as the evaporator region and the two end portions act as the condensing regions.
U.S. Pat. No. 4,931,905, issued to Cirrito et al., discloses two metal plates that have U-shaped grooves so that the plates may form congruent halves wherein matching grooves complete independent heat pipes. A bight section of each heat pipe serves as an evaporator section while the parallel arms of each heat pipe form condenser sections. A wick is positioned within each heat pipe to improve liquid transport when a module is in a non-upright position. The condenser sections are located coincident with the normally upright edges of each module so that, when the module is upright, the vertically disposed condenser sections of the heat pipe gravity-assist liquid transport to the evaporator section.
U.S. Pat. No. 5,283,715, issued to Carlsten et al., discloses a heat pipe structure that is incorporated directly into the metal baseplate of a circuit card thereby eliminating thermal contact resistance between the baseplate and the heat pipe assembly. Components are mounted on a copper circuit layer bonded to a dielectric layer in a first portion of the baseplate with a second portion of the baseplate/heat pipe assembly extending into a heat sink/cold plate condensing area for removal of heat generated in the component portion.
U.S. Pat. No. 6,055,157, issued to Bartilson, discloses a computer module for scalably adding computing power and cooling capacity to a computer system. The computing module includes a first heat pipe assembly having an evaporator plate with an evaporator surface. The first heat pipe also has a condenser in fluid communication with the evaporator plate. The evaporator plate is positioned adjacent one side of a printed circuit board populated with at least one electronic component, or a printed circuit board which has two sides populated with electronic components. When a printed circuit board having components on two sides is used, a second heat pipe having the same construction is positioned adjacent the other side of the printed circuit board so that the electronic components on the other side are positioned adjacent the evaporator surface of the second heat pipe. The evaporator plate of each heat pipe is connected to the condenser by a plurality of necked-down regions. This forms at least one window between the condenser and the evaporator plate of each heat pipe. When more than one heat pipe is used in the computing module, the windows of the various heat pipes align. Electrical connector components can be routed through the windows. The connector component connects the edge of the printed circuit board positioned near the windows.
The present invention provides a thermal bus for cabinets housing high power electronics equipment. In one embodiment, two spaced-apart substantially horizontally oriented evaporators are provided where each is substantially horizontally mounted in a support and positioned in thermal communication with at least one heat generating device. Each of the two elongate evaporators defines a central passageway having a liquid-working fluid entrance port and a vaporous-working fluid exit port and a capillary wick disposed on the walls of the central passageway. A duct defining a central passageway and having a capillary wick disposed on the walls of the central passageway is disposed in fluid communication with the central passageways of the two spaced-apart evaporators A condenser is provided having a vaporous-working fluid entrance port disposed in flow communication with the vaporous-working fluid exit port and a liquid-working fluid exit port disposed in flow communication with the liquid-working fluid entrance port so that a working fluid cycles through the two spaced-apart evaporators, and between the condenser and the two spaced-apart evaporators.
In another embodiment of the invention, a thermal bus is provided for cabinets housing high power electronics equipment that includes two substantially horizontally oriented parallel evaporators interconnected in flow communication with a condenser. Each evaporator is substantially horizontally mounted in a support having a central recess and each having a tube having a capillary wick disposed on an internal surface and being mounted within the central recess of the support. Each of the tubes includes a closed distal end and a closed proximal end with a liquid-working fluid entrance port located at the closed proximal end of the first tube and a vaporous-working fluid exit port located at the closed proximal end of the second tube. A duct defining a central passageway and having a capillary wick disposed on the walls of the central passageway is disposed in fluid communication with the first tube and the second tube. The condenser has a vaporous-working fluid entrance port disposed in flow communication with the vaporous-working fluid exit port of the evaporator and a liquid-working fluid exit port disposed in flow communication with the liquid-working fluid entrance port of the evaporator so that a working fluid cycles; (i) through the two spaced-apart parallel evaporators, and (ii) between the condenser and the two tubes.
In a further embodiment, a system for controlling the heat generated within a cabinet housing high power electronics equipment is provided comprising, in combination, a plurality of circuit boards having heat generating devices disposed on at least one surface and a plurality of substantially horizontally oriented thermal buses. Each thermal bus comprises two spaced-apart evaporators that are each substantially horizontally mounted in a support and positioned in thermal communication with at least one of the plurality of circuit boards. Each of the two elongate evaporators defines a central passageway having a liquid-working fluid entrance port and a vaporous-working fluid exit port and a capillary wick disposed on the walls of the central passageway. A duct defining a central passageway and having a capillary wick disposed on the walls of the central passageway is disposed in fluid communication with the central passageways of the two spaced-apart evaporators. A condenser is provided having a vaporous-working fluid entrance port disposed in flow communication with the vaporous-working fluid exit port and a liquid-working fluid exit port disposed in flow communication with the liquid-working fluid entrance port so that a working fluid cycles; (i) through the two spaced-apart evaporators, and (ii) between the condenser and the two spaced-apart evaporators. A rack is positioned within the cabinet so as to support the plurality of thermal busses and circuit boards in a substantially horizontal relation to the rack.